The Israel Air Force is to decide in a few months between purchasing a third squadron of F-35 fighter jets or the F-15I, which, while less advanced, has other advantages.

The acquisition requires the approval of the General Staff and a ministerial committee, but the recommendation of the air force generally carries the day.

IAF Commander Maj. Gen. Amikam Norkin, who reportedly is leaning toward the F-15, is to submit a recommendation in May.

Israel and the United States agreed last year on the purchase of 50 F-35 fighters, two squadrons, from Lockheed Martin, with delivery completed by 2024.

Nine jets have been delivered so far, and the IAF recently announced that they have reached initial operational capability.

The rapid aging of the IAF’s current fleet makes the new purchases necessary. The air force is still using some fighter planes bought in the late 1970s, and despite a number of upgrades the IAF will retire them.

On the margins of the world economic conference in Davos last week, Prime Minister Benjamin Netanyahu spoke with his Croatian counterpart, Andrej Plenkovic, about the IAF’s sale of F-16s to the Croatian Air Force. Israel closed down its last squadron of F-16A/B last year. The IAF is sill looking for buyers for its F-16C/D jets, and will eventually also have to retire its F-15s.

The F-35, defined as a fifth-generation aircraft, will be the IAF’s future fighter plane.

Senior IAF officers, including the force’s previous commander, Maj. Gen. Amir Eshel, have lavished praise on its capabilities. One of its most important operational capabilities is stealth, the ability to not show up on enemy radar.

But in order employ its stealth capabilities, the F-35 must fly with its bombs inside the plane’s belly, which limits its carrying capacity. If the bombs are carried on the outside of the plane, its stealth capabilities are impaired.

The F-15, though older, has two advantages over the F-35: a longer flight range and the ability to carry larger bombs. Another factor in its favor is that it’s built on a different platform, which means the air force would have a mix of planes rather than relying on a single model.

The F-15I is also cheaper to operate than the F-35. But the plane is currently being upgraded by the manufacturer, Boeing, and its purchase price is expected to rise in any future deal. Thus it could end up costing the same as the F-35 does next time around.

The argument within the air force apparently isn’t over whether a third F-35 squadron is needed, but over how soon it is needed.

Proponents of the F-15 prefer to postpone buying the third F-35 squadron until near the end of the next decade.

The decision is also very important to the competing American manufacturers, Lockheed Martin (the F-35) and Boeing (the F-15), and not only because the deal is likely to be worth almost $3 billion. Boeing is considering closing its F-15 production line, but an Israeli order would keep the line open. It could also persuade other countries to buy the plane, since a purchase by the IAF is considered a seal of approval of a fighter jet’s high quality and continued relevance.

The next squadron will apparently be purchased as part of the military’s next multiyear plan, which will take effect after the current plan ends in 2020. The planes will be bought using American military aid. The U.S. and Israel signed a new 10-year aid agreement in 2016 that will take effect next year.